Lifesteal and physical damage vamp is frekin' everywhere. 2% in the masteries, another 15% on crits in the masteries, 15% phys vamp on red pot, 12% lifesteal on Mercurial, 12% phys vamp on a new top - tier AD item, and 10% on Maw.
Ye standard build includes an IE, BT, a LW upgrade, and 50-80% more crit between TF,PD, SS, Hurricane, Firecannon, and Essence reaver. You might drop BT for Mercurial, or get them both, and you'll probably drop boots.
Most Casters are going to go IE,ER,SS,LW,BT,TF Red Pot- 90% crit, 40% CDR, 50% Lifesteal, 300 bonus AD, 10% MS (slightly slower than boots, slightly faster with phage proc), while corki will drop the upgraded LW for whatever he pleases.
Seriously, ADC's get 30% to 32% lifesteal late game WITHOUT A SINGLE LIFESTEAL ITEM. Admittedly, 15% of this (the red pot) only works against champions.